The invention relates to a method to automatically and accurately portion a sequential flow of objects by weight, using a limited number of simple conveyors and a simple routing mechanism.
Portioning by weight describes the process of selecting a combination of objects from a sequential stream or a fixed pool of objects of known individual weights, to obtain a combination of objects that together will make up a predefined total weight. The objective is to efficiently obtain a reasonably accurate final package weight without having to trim material off any of the objects, thus eliminating waste material.
A variety of methods to automatically portion by weight are in use today, mainly in the fish processing and food industries. They can be grouped into two main categories, listed here by order of increased accuracy:
1) Intelligent batching: A sequential stream of objects is accumulated into a number of holding bins, the objects being weighed and routed to selected bins one at a time. An attempt is made to optimize the bin selection process, usually based on a statistical model of the weight distribution of the infeed objects. The main advantage of this method is the relative simplicity of the equipment required for implementation and fair final Weight accuracy, while the main disadvantage is the requirements for controlled material infeed and inconsistent final weight accuracy.
2) Precise portioning: Objects are selected from a sufficiently large random-access pool of objects of known individual weights to ensure that a satisfactory combination of objects can be found. Random access relates to the ability of the equipment to route any object, or combination thereof, to an accumulation station for the final portion. The main advantage of this method is high and consistent final weight accuracy. The main disadvantages are the complexity of the equipment required for implementation and the requirement for complex and controlled material infeed to fill the vacated object pool positions.
Random access to a large pool of individual objects with known weights has been a requirement for precise portioning, but the random access requirement has only been achieved using relatively complex equipment. Sequential access to such a pool of objects requires only simple equipment for implementation (a conveyor), but an inherent problem with sequential access is how to dispose of objects in the sequence that have not been selected for a portion combination. Usually such objects have to be rejected or recirculated back to the infeed stream.
Patents have been issued for three precise Portioning by Weight methods (DE 44 04 897 A1, U.S. Pat. No. 4,446,938 and U.S. Pat. No. 4,660,661) but they are all based on a random access to objects. The invention described here, on the other hand, is based on a sequential access to objects with known weights.
Two patent applications are known that relate to methods for batching a sequential stream of objects into batches with a predetermined weight with reasonable accuracy. Application GB 2116732A relates to the use of statistical methods, based on a normal weight distribution among the objects to optimize the selection process. A disadvantage of this invention is the fact that objects of an unsuitable weight that cannot be used as part of a portion when they happen to pass through the selection process, have to be rejected or recirculated back to the input stream. Application WO 9608322A1 relies on identical harware and also uses statistical methods to optimize the selection process. Unsuitable objects also have to be rejected or recirculated, but novely is claimed for the use of the actual weight distribution which refines the selection process and negates the problem of having an input stream of objects that does not have a normal weight distribution, e.g. due to prior removal of objects more suitable for other processing.
The objective of the invention is to automatically achieve satisfactory portioning accuracy using a strictly sequential access to a pool of individual objects with known weights, requiring only simple equipment for implementation. The invention, called Flow Portioning, is based on a unique method of disposing of objects in the sequence that are not part of the pending portion, by using them as a part of subsequent portions to be processed.
One implementation of the equipment according to the invention is to use a long conveyor to hold and transport a pool of objects with known weights towards a selection station. The length of the conveyor is determined only by the size of the pool required to achieve a satisfactory combination of objects for precise portioning.
Another implementation of the equipment according to the invention is to use two or more synchronized conveyors, mounted and driven in parallel, to increase throughput and reduce the length of the equipment. In this implementation, each conveyor will have an individually actuated selection station, but portion accumulation stations in common with the other conveyors.